Four classes of biological molecules are known, namely, those comprising proteins, lipids, carbohydrates and nucleic acids. Nucleic acids, in turn, comprise two subsumed classes: DNA which is a genetic component of all cells, and RNA which usually functions in a synthesis of proteins.
The purview of the present invention extends to biomolecules, generally, but a working point for the sake of pedagogy is now established by referencing biomolecules comprising DNA. DNA is emphasized because it is the prime genetic molecule, carrying all hereditary information within chromosomes.
DNA stands for deoxyribonucleic acid. The DNA of most cells resides in a cell's nucleus. Its structure comprises long chains of relatively simple molecules called nucleotides. Each nucleotide comprises three parts: (1) a phosphate group stripped of one special oxygen atom; (2) a sugar called "ribose"; and (3) a base. It is the base alone which distinguishes one nucleotide from another- thus it suffices to specify a base to identify a nucleotide. The four types of bases which occur in DNA nucleotides are adenine (A); guanine (G), cytosine (C) and thymine (T).
A single strand of DNA comprises many nucleotides strung together like a chain of beads. DNA usually comes in double strands, that is, two single strands which are paired up, nucleotide by nucleotide, in the form of the well known DNA double helix.
DNA carries a vast array of information through its nucleotide sequence. Accordingly, the order of nucleotides (considered as a linear progression e.g., "A T T C G G A C C . . . ") is highly varied. A nucleotide sequence may comprise inter alia a single nucleotide, a duplet (adjacent pairs of bases), a codon (three consecutive bases), a gene (a portion of a strand which codes for a single enzyme), a strand of arbitrary nucleotides, or a genome comprising a total set of DNA molecules for an organism (e.g., 3.times.10.sup.9 nucleotides for a human cell).